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Allow T[N] where N is numeric and T has apparent numeric index signature

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This commit is contained in:
Anders Hejlsberg 2017-01-16 12:18:01 -08:00
parent 3b0f2c152b
commit 919e682e3f
1 changed files with 16 additions and 6 deletions
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22
src/compiler/checker.ts
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@ -16032,14 +16032,24 @@ namespace ts {
}
function checkIndexedAccessIndexType(type: Type, accessNode: ElementAccessExpression | IndexedAccessTypeNode) {
if (type.flags & TypeFlags.IndexedAccess) {
// Check that the index type is assignable to 'keyof T' for the object type.
const objectType = (<IndexedAccessType>type).objectType;
const indexType = (<IndexedAccessType>type).indexType;
if (!isTypeAssignableTo(indexType, getIndexType(objectType))) {
error(accessNode, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(objectType));
if (!(type.flags & TypeFlags.IndexedAccess)) {
return type;
}
// Check if the index type is assignable to 'keyof T' for the object type.
const objectType = (<IndexedAccessType>type).objectType;
const indexType = (<IndexedAccessType>type).indexType;
if (isTypeAssignableTo(indexType, getIndexType(objectType))) {
return type;
}
// Check if we're indexing with a numeric type and the object type is a generic
// type with a constraint that has a numeric index signature.
if (maybeTypeOfKind(objectType, TypeFlags.TypeVariable) && isTypeOfKind(indexType, TypeFlags.NumberLike)) {
const constraint = getBaseConstraintOfType(<TypeVariable | UnionOrIntersectionType>objectType);
if (constraint && getIndexInfoOfType(constraint, IndexKind.Number)) {
return type;
}
}
error(accessNode, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(objectType));
return type;
}